Measuring instruments are frequently used in automation engineering for monitoring a medium or, as the case may be the properties of a medium. In this connection, the filling level, the pressure or the temperature of the medium in a container are measured. Such measuring instruments mostly consist of a bottom part designated as process connection and a housing placed thereon as an upper part, which is mainly used as a protection for the sensor and the associated electronics. The process connection connects the measuring instrument to a container or, as the case may be to a pipeline or, as the case may be to a connecting piece and usually contains the sensor element as such. The sensor element is, for instance, configured as a piezoresistive or capacitive measuring cell in pressure measurement instruments.
In order to connect the measuring instrument to the equipment or, as the case may be, to the container containing the medium to be measured, sleeve-like adapters have proven advantageous, such as they are, for instance, described in the German specification DE 196 28 551 B4. These adapters have a through-hole that extends in the axial direction and a circumferential sealing web configured as a spring web. The measuring instrument is usually screwed into the adapter, the bottom part of the measuring instrument, i.e. the process connection, being in contact with the circumferential sealing web. The contact pressure between the process connection and the sealing web can be defined by screwing in the measuring instrument with a specific torque.
In some applications, it has proven to be advantageous to realize the connection between the process connection and the adapter without an additional sealing element because a separate seal is a losable component, on the one hand, which represents another cost factor as such, and on the other hand tolerances are consequently also added up. Without the additional sealing element, the contact surfaces of the process connection and the adapter form a so-called metal-metal seal. Connections with such a sealing concept are in fact not suitable for frequently releasing the connection, which can be disadvantageous for the inspection and maintenance work to be carried out.